For over a century, radio wave signals have been transmitted using conventional antenna structures. In contrast to radio science, electrical power distribution has relied on guiding electrical energy along electrical conductors such as wires. This understanding of the distinction between radio frequency (RF) and power transmission has existed since the early 1900's.
Radio frequency identification (RFID) systems, however, have used RF energy that is emitted from a reader device to power tags. The tags may affect the emitted signal to invoke a change in the emitted signal that is detectable by the reader device or the tags may transmit an RF signal that is detectable by the reader device. In the former case, the reader may be able to determine that a tag is within an operable range of the reader device. In the later case, the reader may be able to extract a code that uniquely identifies the tag from the signal output by the tag. The range of RFID systems is severely limited. Also, the capabilities of the tags are limited due to the small amount of useable energy that may be derived from the RF signal emitted by the reader device.